Cannabinoids No Help for Cancer Pain, Concludes Meta-Analysis

Nick Mulcahy

January 29, 2020

When added to opioids, cannabinoids in an oral spray were no better than placebo in reducing cancer pain in adults with advanced disease, concludes a new meta-analysis.

It included five randomized controlled trials from the United Kingdom and Europe, and involved a total of 1442 patients.

"Cannabinoids cannot be recommended for the treatment of cancer-related pain," the authors conclude.

The results were published online on January 20 in BMJ Supportive & Palliative Care.

The finding throws some cold water on a hot topic, as cannabinoid use for cancer pain has been reported by about 20% of patients in two recent surveys, the authors note.

"There is an increased recent interest in cannabinoids (including cannabis) for [cancer] pain management" as legislative changes have occurred in many countries, writes senior author Jason Boland, PhD, FRCP, Wolfson Palliative Care Research Centre, Hull York Medical School, UK, and colleagues. He said some patients with advanced cancer he sees report taking cannabinoids, but he does not prescribe them.

Medicinal use of cannabis is legal in 40 countries and 29 US states. But, as cancer pain guidelines by the World Health Organization state, data analysis is needed.

The meta-analysis focused on chronic pain among advanced cancer patients.

"I don't know of any data showing cannabinoids work for acute pain," Boland told Medscape Medical News.

The product that was evaluated in studies included in the meta-analysis was a pump-action oromucosal spray that used 1:1 tetrahydrocannabinol (THC): cannabidiol (CBD) extracts (two of the many cannabinoids in cannabis).

The oromucosal spray product is not available in the United States, pointed out Erica Rhein, PharmD, University of Colorado Cancer Center, Aurora.

She explained that there is a "huge" variety of THC and CBD combination products in various strengths and ratios, as well as a multitude of ways to administer or ingest them.

The new analysis shows that a specific product did not improve patients' self-rated pain intensity, remarked Rhein. "However, this conclusion cannot really be extended to all cannabinoid products because they simply have not been studied in the same manner."

That said, she added, "studying every single product available on the market is not feasible."

The new study builds on a systematic review by German researchers (Schmerz 2019;33:424-436). Both efforts had the same overall conclusion, but the new work is based on additional methodological information, and thus, is supported by higher-quality evidence, say Boland and colleagues.  

A Nuanced Question and More

The primary outcome of the meta-analysis was the change in average numeric rating scale pain scores (mean difference, −0.21; P = .14), which showed no difference between the cannabinoid and placebo groups.

Importantly, cannabinoids had a higher risk of adverse events compared with placebo, especially somnolence (odds ratio [OR], 2.69; P < .001) and dizziness (OR, 1.58; P = .05). Dropouts and mortality rates were high.

Commenting on the finding, Rhein emphasized that cancer pain is a complex phenomenon, and she wondered if there were any subsets of patients who might have benefitted from cannabinoids.  

Rhein observed that "psychological and spiritual factors can play a big role" in a patient's pain. "I would be interested to know if there was a particular subset of patients that seemed to benefit most...For example, does someone with anxiety, depression, or a history of cannabis use perceive more benefit from cannabinoids for his or her pain versus a patient without those additional factors?"

The meta-analysis does not answer "nuanced questions such as this," she commented.

Boland and coauthors, as well as Rhein, have reported no relevant financial relationships.

BMJ Support Palliat Care. Published online January 20, 2020. Abstract

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